The Strike Zone

The only thing predictable about lightning is how scary and potentially destructive it is.

Issue 144: May/June 2022

Joe Miano was relaxing on the deck of his Endeavour 42, Bonzee, in a Punta Gorda, Florida, marina during the evening of what had been a stormy Independence Day. He was there to watch the annual fireworks display, which went on despite some thunder and rain, when Bonzee’s mast suddenly lit up blindingly white to the chest-thumping roar that accompanies a lightning strike.

Though Joe was unharmed physically and the boat suffered no structural hull damage, all of its electronics were fried, resulting in four months in the boatyard (where I met him and his wife, April) and tens of thousands of dollars of repairs, thankfully covered by insurance, before the Mianos could get back on the water.

Florida is the lightning capital of the U.S., but lightning strikes can happen anywhere and they’re not uncommon, as I can attest: my Ericson 38-200, Walden, was also hit while under contract for purchase, causing extensive damage to the electrical systems. Beyond hurricanes, violent line squalls, or sinking, lightning is probably the most terrifying phenomenon a sailor will experience—if only because of its sublime power and unpredictability.

An Unstoppable Force

Simply put, lightning happens when negatively charged particles within an ionized cloud escape the cloud and travel to the positively charged ground beneath it. Lightning strikes occur when opposing particles become so charged that an electrical arc connects, despite air acting as an insulator. Here’s how the National Weather Service (NWS) explains it:

“Eventually, when the charge difference between the negative charge in the cloud and the positive charge on the ground becomes large, the negative charge starts moving toward the ground. As it moves, it creates a conductive path toward the ground. This path follows a zigzag shape as the negative charge jumps through segments in the air. When the negative charge from the cloud makes a connection with the positive charge on the ground, current surges through the jagged path, creating a visible flash of lightning.”

Lightning manifests in two primary ways: cloud-to-cloud and cloud-to-ground. Cloud-to-cloud lightning does not strike the earth (some people call it heat lightning, though the NWS says heat lightning “is just lightning from a thunderstorm that is too far away for any thunder to be heard.”) What sailors need to worry about is cloud-to-ground lightning, which, as the name implies, does strike the earth.

Direct strikes occur when the electrical current is discharged by only one major electrical arc. Side strikes happen when an object nearby a direct strike is also struck, when lightning—which will use all available conduits—arcs from the nearby charge to the attractive object, seeking an additional path to ground.

Direct strikes are much more serious for sailboats than side strikes, which would likely only cause damage to onboard electrical systems. When lightning strikes a sailboat, the lightning seeks an uninhibited path from cloud to ground (sea), and the boat’s mast simply acts as an electrical conduit for up to one billion volts of electricity that will create a path if a predefined one does not exist.

Unlike conductors such as silver, copper, or aluminum, which let electrical current flow unabated without resistance, air is an insulator and a poor conductor of electricity. Pretty much everything that sailboats and their masts are made of—including fiberglass—are preferable paths for lightning than air.

Resistance, measured in ohms, causes an electrical circuit to heat up, which is why trees or wooden masts—while technically conductors—tend to explode or vaporize during lightning strikes. Carbon fiber and fiberglass—both of which are preferable lightning paths than air—are similarly subpar conductors of lightning’s massive amounts of energy. So, it’s not uncommon for carbon fiber masts, as well as fiberglass hulls, to be either entirely vaporized or peppered with millions of small holes after a lightning strike. Aluminum masts, and steel rigging to a lesser extent, are excellent conductors, allowing electricity to move with less resistance.

Water makes a difference too. Saltwater is an excellent conductor of electrical current, so sailboats in saltwater generally suffer far less hull and deck damage than their freshwater counterparts. Holes in the hull, resin turned to dust within a fiberglass laminate, charred core material in deck laminates, and other catastrophic horror stories are far less likely in salt or brackish water than in freshwater.

Providing a Path

No foolproof method exists for preventing or even protecting one’s boat entirely against lightning strikes. That said, the traditional school of thought from the American Boat and Yacht Council (ABYC) and those in the marine industry is to ground the mast and rigging to the keel via heavy-gauge wire.

On a monohull with a bolt-on keel, which acts as a large ground for electrical current to pass through, this is easily accomplished by tying the mast to a keel bolt with 2/0 AWG copper wire. On a boat with an encapsulated keel, it’s common practice to bolt a copper ground plate made for lightning protection— not an SSB radio—directly to the metal ballast by grinding through the fiberglass encapsulation in one area. A ground plate should be affixed to either side of the hull as close to the waterline as possible, because lightning typically seeks an exit at or near the waterline.

If no predetermined path is available, lightning will create its own path, which may prove catastrophic. Anecdotal evidence has shown that wood vessels in particular—with no predetermined path from mast to ground—are susceptible to holes blowing through the hull. Fiberglass vessels generally fare better, but a lightning strike can vaporize a hull’s resin or create a galaxy of pinholes. Metal boats are the most likely to be struck yet the least likely to suffer hull damage, because the entire hull acts as a grounding plate.

Bonzee, a fiberglass boat with an encapsulated keel, was berthed in the brackish waters of Punta Gorda on Charlotte Harbor. She had recently undergone an extensive refit that included common bonding of all bronze through-hull fittings and grounding her mast to a copper plate beneath the waterline with heavy-gauge cable for lightning protection. She escaped the lightning strike with no perceivable structural damage.

But nearly every electronic device connected to the AC and DC electrical circuits was destroyed and had to be replaced. The carnage included the following on the DC side: the DC breaker panel (breakers welded in the middle position), Simrad VHF radio and antenna, Simrad AIS transponder, Garmin chart plotter, Fusion stereo and amplifier, B&G multifunction displays and tridata transducers (wind speed/direction, depth, temperature), all exterior lighting, all onboard fuses, all cabling in the mast, mast ground wire, mast actuator, and electric furler motor. On the AC side, all GFCI outlets, wiring, battery inverter/charger, and the 30-amp power cord itself were destroyed.

In the case of Walden, the 1987 Ericson 38-200 my wife, Avery, and I were under contract to buy, we were about to get in the car to head over for the survey when the seller called me. “Drew,” he said, sounding rather bewildered, “you’re not going to believe this, but Kismet was hit by lightning.”

Though the lightning strike slowed the process, we decided to proceed with the pre-purchase survey with the understanding that we would pay a reduced, as-is price. After Kismet became our Walden, we discovered that the lightning had arced from the aluminum mast step through the keel via the stainless steel keel bolts. Near the rudder stock, we found a hole in the fiberglass that led us to believe that lightning had exited at the rudder stock bushing as well, perhaps a result of a side strike from the nearby backstay.

The common bonding of components in the mast-to-keel grounding system—including tanks, metallic through-hulls, and wire rigging—can prevent the unpredictable arcing that can occur between metal fixtures known as a side strike. On Walden, neither these components nor the mast were bonded to one another and the keel, causing the lightning to create its own path. However, she suffered no detectable structural damage, perhaps due to her large aluminum mast, mast step, large stainless steel keel bolts, and exposed lead keel.

We later discovered the strike had entered via the masthead VHF antenna, which lay vaporized in charred pieces on deck, and proceeded to wreak havoc on the DC side of Walden’s electrical panel. The VHF radio, wind instruments, stereo, chart plotter, and autopilot were all destroyed, due either to current overload or simply being in close proximity to an electromagnetic pulse (EMP) event—a short, intense burst of electromagnetic energy that can occur with a lightning strike. The AC side—consisting of power outlets, marine fridge, shorepower, battery charger, and a water heater—was spared entirely.

We found vaporized bilge gelcoat and fiberglass where the masthead coaxial connector lay. While inspecting our hull, which had many large blisters that we later fixed, our surveyors told us they had seen a high incidence of hull blisters in boats that had reported lightning strikes, perhaps the result of resin becoming super-heated, leaving the underlying laminate dry.

Advances in Protection

Lightning is the most capricious and least understood natural phenomenon a sailor will face. All of the recommended procedures and standards canonized by professional marine bodies like the ABYC are based on anecdotal evidence and everevolving scientific theory, as lightning is a force so powerful that it cannot be duplicated, manipulated, and tested in the laboratory’s confines.

Short of purchasing a sailboat boat with a metal hull—or a fiberglass boat with an aluminum mast and bolt-on lead keel, with all rigging wires and metal components bonded downward with no 90-degree kinks or bends to the keel or propeller shaft—there is little one may do other than hope and pray. Despite this grim reality, experimental surge-protecting devices proven in landbased applications such as cellular towers are now being used on recreational boats.

For example, on Walden’s masthead VHF coaxial cable, we installed a device known as a gas-block surge protector, which splices into the coaxial cable that travels down the mast and into the boat’s electrical panel. This disconnects the coaxial cable’s circuit in the event of a large electrical surge and instead diverts the power surge to ground— on Walden, the lead keel.

Likewise, a transient voltage surge suppressor (TVSS) similarly disconnects a circuit in the case of a large surge of electrical current. We wired a TVSS into our NMEA 2000 instrument circuit to protect our wind and depth instruments, radar, chart plotter, and autopilot. Another TVSS protects the VHF radio circuit. To ensure current could not travel down the mast and into the boat’s electrical circuits, we used a wireless B&G wind transducer rather than a wired unit. As backup, we also installed a VHF antenna mounted on the stern rail with an additional gas-block coaxial surge protector device. Beyond these measures, the best we can do is watch the weather and try to avoid looming storms.

If you can’t get out of the way and you can’t leave your boat in an electrical storm, stay below and away from metallic components. Put your handheld electronic devices in an oven, which will, in principle, serve as a Faraday cage to protect them. And before any of this happens, purchase comprehensive insurance that will replace gear destroyed during a strike.

Drew Maglio is a writer, tutor, and the owner and operator of Capital Boat Works, a marine repair, detailing, consulting, and training company based in Annapolis, Maryland. Hailing from South Florida, Drew has loved sailing and boating since he was a youngster. He has owned, worked on, and restored boats from 12 to 38 feet.

 

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